1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus and a charging device.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a charged photoconductor with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor (image carrier) on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet, followed by heating and pressurization, whereby an image is formed on the sheet.
In the above-mentioned image forming apparatus, when the surface of the photoconductor is uniformly charged by a charger, products called discharge products such as ozone and nitrogen oxide are generated by the electrostatic discharge of the charger. The discharge products such as ozone and nitrogen oxide attach to the surface of the photoconductor, and bind to water molecules in the atmosphere. Consequently, the electric resistance on the surface of the photoconductor is reduced, and image defect (image flow) may be caused.
Under such a circumstance, to prevent image flow from occurring, a technique of outputting discharge products floating around a charger has been proposed.
Japanese Patent Application Laid-Open No. 2012-198490 discloses an image forming apparatus including: jetting means for jetting gas toward a charging section that charges a photoconductor or toward a region around the charging section; and sucking means for sucking gas including the gas jetted by the jetting means around the charging section.
Japanese Patent Application Laid-Open No. 2008-76777 discloses an image forming apparatus including: an air-intake duct that guides gas to the inside of a charger; an air-intake fan that sends the gas from the outside to the air-intake duct; an exhaust duct for outputting gas from the inside of the charger; and an exhaust fan that sends to the outside the gas from the exhaust duct, in which the velocity of air in the air-intake duct resulting from the operation of the air-intake fan is greater than the velocity of air in the exhaust duct resulting from the operation of the exhaust fan.
Japanese Patent Application Laid-Open No. 10-198128 discloses a corona discharging device including: a shield case that covers an electrostatic discharge wire for corona discharging to a charge target, and has an air-blowout port opened along the electrostatic discharge wire; an air duct that connects the air-blowout port with the outside of the apparatus housing; and an air blow fan that blows the air on the outside of the apparatus housing into the shield case through the air duct and the air-blowout port. In the technique disclosed in Japanese Patent Application Laid-Open No. 10-198128, a partition wall is uprightly provided along the longitudinal direction of the shield case in the air duct, thereby temporarily increasing the pressure of the air flow sent toward the shield case on the near side of the partition wall. In this manner, the air flow is uniformized along the longitudinal direction of the shield case when it passes over the partition wall, and is thus uniformly blown into the shield case.
However, in the techniques disclosed in Japanese Patent Application Laid-Open Nos. 2012-198490 and 2008-76777, the direction of the air flow toward the charging section may become inconsistent when discharge products are output by gas (air). When such inconsistency of the direction of the air flow is caused, the air containing discharge products does not smoothly flow toward the exhaust duct, and as a result, some of the discharge products are not output. Consequently, image flow cannot be sufficiently prevented.
On the other hand, in the technique disclosed in Japanese Patent Application Laid-Open No. 10-198128, since an air flow is uniformly blown to the air-blowout port, an air flow can be uniformly blown along the direction in which the electrostatic discharge wire is provided. However, at the position where the partition wall is uprightly provided, the area of the air-sending port is small and the pressure loss (ventilation resistance) of the air flowing through the inside of the duct is undesirably large. Thus, the volume (air velocity) of the air blown to the electrostatic discharge wire is small, and the performance for outputting discharge products cannot be sufficiently ensured.